The goal of the Yale Virology Training Program is to equip predoctoral trainees with the intellectual and research foundations necessary to become independent scientists/educators investigating the molecular biology of viruses, host responses to them, and their roles in human disease. The Virology Training Program combines rigorous research training in a highly collaborative, interactive environment with a thorough academic program of instruction in modern virology, general microbiology, immunology and related disciplines. The program offers training in virtually all aspects of viral genetics, the molecular, cellular and structural biology of viruses, as well as virus-host interactions at the cellular and organismal levels. Areas of particular strength include the structural biology of viral components, viral transformation, viral entry, trafficking and replication, and the adaptive and innate immune response to viruses, including a number of select agent pathogens of biodefense interest. As a group, the 19 Virology Program trainers have an outstanding record of research accomplishment and training and many are national or international leaders in their fields. These faculty have primary appointments in 12 different Yale departments and currently have 50 predoctoral virology trainees working in their labs. Predoctoral training leading to the Ph.D. degree involves formal course work in microbiology and/or immunology, as well as other areas of biology, research rotations, teaching, and the qualifying exam in the first three semesters, with dissertation research beginning in year one and becoming the primary focus of activity after completion of the qualifying exam. Intensive training in the methods, logic, and responsible conduct of research are supplemented with a wide array of opportunities for scientific interactions. The median time to obtain the Ph.D. degree is 5.7 years. Yale Graduate and Medical Schools, and Virology trainers make extensive efforts to attract and retain trainees from diverse backgrounds, particularly under-represented minority groups. This application requests funding to continue support for four predoctoral trainees in each year. Trainees will supported by this grant for a maximum of two years.